Decouplers

Ive got a freaking annoying problem. The thing is that the decouplers dont push with enough force so that the empty fuel tanks and engines fall onto my next stage so half of the rocket explodes ruining the whole launch. Is there a design issue or are they buggy right now?

that isn't an uncommon issue. Are you refering to the inline or the radial decouplers. In terms of the inline decouplers, there is minimal force output from those. If they are colliding, you have another issue from a stage imbalance or severe wobble. As for the radial decouplers, placement is important. If you have them mounted at the top/bottom of a booster, it will cause it to rotate on ejection, sometimes causing the bottom/top to swing into your rocket. This can be countered by setting up your radial decoupler to be on a middle fuel tank and building your tanks both up and down from it. This will keep it more vertical. Another thing is use the small separation engines. On large tank stacks, I find that four per stack works well. Have two on top and two on bottom pointing mostly vertical, but slightly angled away from your rocket. (have one on each side) This pushes large tank stacks out. You can set separation engines to fire on decoupling if they are in the same stage.